1. Field of the Invention
This invention relates to a sheet supply device for use in a reproduction device, such as a printing device or a copying machine. More particularly, the invention relates to a sheet supply device for enabling an image to be formed at a predetermined position on a sheet through a reproduction operation, such as a printing operation or a copying operation.
2. Description of Related Art
FIG. 5 shows a conventional sheet supply device for use in a reproduction device, such as a printing device or copying machine. As shown, a sheet supply device 40 comprises a pair of sheet feeding rollers 7, a sheet detection sensor 9 for manually-inserted sheets 18, a pair of sheet supply rollers 11 for manually-inserted sheets 18, a cassette sheet supply roller 13, and a sheet supply cassette 17. At the left side of the sheet supply device 40 are an opening 40A, through which the sheet supply cassette 17 is insertable, and a feeder 19, through which a sheet is manually insertable. In addition, the sheet supply device 40 includes therein a sheet supply passageway 21 through which a manually-inserted sheet 18 from the feeder 19 is fed to the sheet feeding rollers 7, a sheet supply passageway 23 through which sheets 15 stacked in the sheet supply cassette 17 are individually fed to the sheet feeding rollers 7, and a sheet supply passageway 25 through which the sheet 15 or the manually-inserted sheet 18 is further fed by the sheet feeding rollers 7.
In this sheet supply device 40, the sheets 15 stored in the sheet supply cassette 17 in a stack form are individually separated from one another and fed through the sheet supply passageway 23 to the rollers 7. The manually-inserted sheet 18 fed through the feeder 19 is detected by the manually-inserted sheet detection sensor 9 and fed through the sheet supply passageway 21 to the sheet feeding rollers 7 by the sheet supply rollers 11. The sheet 15 or the manually-inserted sheet 18 is nipped by the pair of rotating sheet feeding rollers 7 and fed toward a sheet supply completion position 29.
In this sheet supply device 40, in order to accurately form an image at a predetermined position on a sheet in this device 40, the position of a tip portion of the fed sheet 15 or 18 must be accurately located at the sheet supply completion position 29. Therefore, the contact point between the pair of the sheet feeding rollers 7 is used as a reference position 28. The sheet detection sensor 5 for detecting the sheet 15 or 18 is provided at a predetermined position in the sheet supply passageway 25 between the reference position 28 and the sheet supply completion position 29 located a predetermined distance from the reference position 28. When the tip portion of the fed sheet 15 or 18 is detected by the sheet detection sensor 5, the sheet 15 or 18 is further fed toward the sheet supply completion position 29 a predetermined amount by the sheet feeding rollers 7. So, the tip portion of the sheet 15 or 18 is located at the sheet supply completion position 29. Accordingly, this sheet supply device is designed to be hardly influenced by a feeding error of the sheet 15 or 18 due to positional deviation of the sheet or due to sheet slippage during a feeding operation of the sheet by the rollers 11 and 13.
However, frequently the sheet detection sensor 5 is not accurately secured at the predetermined position of the sheet supply passageway 25. Therefore, even when the sheet 15 or 18 is fed toward the sheet supply completion position 29 by a predetermined amount after the sheet 15 or 18 is detected by the sheet detection sensor 5, the tip portion of the sheet 15 or 18 is fed to a deviated position that differs from the sheet supply completion position 29 by an amount corresponding to sensor 5 securing error. As a result, an image can not be accurately printed or copied at a predetermined position on a sheet 15 or 18.
In addition, the sheet detection sensor 5 has an inherent read-out (detection) error itself. The same positional deviation problem as described above will also occur due to this error.